RE: Red warning light "Battery/Alternator" on 2004 C230 Kompressor (37,000 miles). I read all the threads on this posting earlier-most of all answers were about the battery, how to properly change the battery, and/or resynching some of the electrical issues/features. I have NO problem with starting the car - my red warning light is probably more about the Alternator. Was told IF I needed an alternator-it would be about $900 for a new Bosch ! Parts only, and add 2.5 hrs. for labor. Could this light be coming on for ANY other REASON?? I am supposed to take a road trip and don't want problems when not at home. Ugh. Any answers and prayers(haha) would be greatly appreciated. Carolyn in Ft. Laud.

Starting with a code reader to find out the error codes. Then, decide on what you should do.
Replacing the battery may help. But if you can start the car consistently, then your battery should be fine.

Replacing the battery can be tricky. If you are not confortable in doing it, you should get a good mechanic to give you a quote. If not done properly, other expensive components (like computer) might be at risk.

Resynch your settings: your dealer may be able to help out as some of the instructions are listed in the owner manual.

Subject to these results it will confirm whether the alternator (voltage control unit) is OK or not.

Post results and I will give my prognosis.

Assuming that the voltage control is bad and under delivering it won't be long before the car won't start!

If you totally flatten the battery you will also damage that.

Alternatively get a competent electrician to do the checks I have suggested.

You should be able to go to a Bosch dealer and get your alternator exchanged or repaired rather than buying a complete new component (if you are looking for minimum cost repair). A new Bosch alternator will be quality assurred however.

I got same problem and driving with it for half a year. The battery is not getting dead but I would also like toeliminate the problem. My voltages are 12.47 V when off, in idle (~850-900 RPM) it is 13.85 V, at 2K RPM - 14.22 V. Pls advise what is the problem and whatcould I do bymyself. Pls help.

Quote:

ORIGINAL: snanceki

Yep sounds like the alternator has gone bad.
Simple check before spending lots of money.
Voltage at battery terminals with ignition off. battery voltage at idle. Battery voltage at say 2000 rpm.
Subject to these results it will confirm whether the alternator (voltage control unit) is OK or not.
Post results and I will give my prognosis.
Assuming that the voltage control is bad and under delivering it won't be long before the car won't start!
If you totally flatten the battery you will also damage that.
Alternatively get a competent electrician to do the checks I have suggested.
You should be able to go to a Bosch dealer and get your alternator exchanged or repaired rather than buying a complete new component (if you are looking for minimum cost repair). A new Bosch alternator will be quality assurred however.

Mine was going the same thing! I had the battery tested and it ended up being the alternator b/c when the I replaced it it was fine! I bought the alternator from auto zone for $250 with a lifetime warranty and had a local mechanic install it for $90! Talk about saving some money from the dealership!. Its been running fine for a few months but I bet thats what your prob. is. take it to auto zone and have the run a free diagnostic on the battery. The alternator in my 2001 C320 was easy to get to. Call round and get quotes on labor you should be able to get it fixed cheaper.

I have an 04 C230K and it started aboput 40K and only during the cold months. It stopped after summer came and then it started back up again this winter (now I have 70k on car). I wrotwe a thread about it trying to figure out what the heck it was. I know it's not the battery and the alternator was charging fine at normal temps. It seemd to only do this at cold starts and once the car warmed up it was fine. It casued all my lights to glow (ABS, SRS, BAS) none of the windows, locks, radio, air, sunroof would work while it did this. SO I took it to a mechanic and let them keep it over night to test the alternator on a cold start. Well they found that the alternator was spiking out at 18V which is real bad for the car and can eventually fry the computer system. SO thanks to this forum I bought a new Voltage regulator online for $122 (Valeo) it was actually a genuine part from MB and they wanted $188 for it. So I replaced it this past weekend and the car works just fine now.!

SO DON'T CHANGE THE $700 ALTERNATOR! JUST GET A VOLTAGE REGULATOR FOR IT! YOU WILL SAVE A LOT OF $$$$$$

re: Red warning light "battery/alternator" on 2004 c230 kompressor (37,000 miles). I read all the threads on this posting earlier-most of all answers were about the battery, how to properly change the battery, and/or resynching some of the electrical issues/features. I have no problem with starting the car - my red warning light is probably more about the alternator. Was told if i needed an alternator-it would be about $900 for a new bosch ! Parts only, and add 2.5 hrs. For labor. Could this light be coming on for any other reason?? I am supposed to take a road trip and don't want problems when not at home. Ugh. Any answers and prayers(haha) would be greatly appreciated. carolyn in ft. Laud.

hey my 2002 c320 was doing the same and eventually i determined it was the alternator when the battery tested good as well as the connections. It got to the point where my car would die though after bout a week of the light popping up. I bought the alternator part at auto-zone with a lifetime warranty for $279 so it's under my name not the mechanics when it goes out in the future and then i called around getting an estimate on labor alone and had it put in at a trusted local mechanic for $89! It looks like a simple procedure its been going strong for a year now and saved me lotss of $$$ not taking it to the dealership. Buy your own part at your local auto store to save serious cash if money is an issue & call around on prices the alternator is easy easy to replace.

The Voltage Regulator is part of the alternator. The Alternator isn't the problem. If you look at the back side of the alternator there is a plastic shield there (where the wires goes into) that is where the Voltage Regulator is. There are 2 tiny screws for the plastic shield(covering) and then 3 bigger ones for the actual voltage regulator(the wires plug into this part). I just did it a few weeks ago and haven't had the issue since (when I was having it everyday).